a. Field of the Invention
The present disclosure relates to intracardiac catheter location and imaging, and among other things, the present disclosure relates to the combination of intracardiac images from multiple imaging modalities and utilizing structures present in each image to more accurately produce composite images.
b. Background Art
Electrophysiology catheters are used in a variety of diagnostic and therapeutic medical procedures to correct conditions such as atrial arrhythmia, including for example, ectopic atrial tachycardia, atrial fibrillation, and atrial flutter. Arrhythmia can create a variety of dangerous conditions including irregular heart rates, loss of synchronous atrioventricular contractions and stasis of blood flow which can lead to a variety of ailments or death.
In a typical procedure, a catheter and sheath are manipulated through a patient's vasculature to a patient's heart. The catheter carries one or more electrodes which may be used for mapping, ablation, or other treatments. Once positioned, treatment may include radio frequency (RF) ablation, cryoablations, lasers, chemicals, high-intensity focused ultrasound, etc. An ablation catheter imparts energy to the cardiac tissue to create a lesion that disrupts undesirable electrical pathways, thereby limiting or preventing stray electric signals leading to arrhythmias. The position of the ablation catheter within the heart can directly affect the physician's ability to accurately and effectively perform an ablation procedure.
Two catheter based imaging modalities are commonly used in electrophysiology procedures, the first being intracardiac echo (“ICE”) that produces an echo image displaying structures within an echo plane emitted from the catheter. Traditionally, ICE catheters do not contain electrodes and their orientation and position are determined with reference to landmark structures visible in the echo image in conjunction with other imaging modalities such as fluoroscopy, magnetic resonance imaging (“MRI”), or computed tomography (“CT”) models.
Location of the ICE catheter using fluoroscopy can involve several drawbacks, the first being that the images produced through fluoroscopy are two dimensional and include overlay of all intervening tissue and bone structures, which can obstruct the areas of interest. Without a third dimension, navigation and location of the ICE catheter can be challenging. The second drawback is the patient's exposure to doses of radiation in the course of a procedure.
Both MRI and CT devices are capable of producing a geometric model of cardiac structures, yet neither can do so in real time during a procedure utilizing an ICE catheter. Instead, both create a model which can serve as a general reference in which the position of the ICE catheter can be located generally, but may not provide the desired specificity for use during cardiac procedures. Thus, it can be difficult to place an ICE catheter in the position and orientation needed to generate an image of a specific structure of interest.
The second imaging modality commonly employed is a three dimensional physiological visualization, navigation, or mapping system that uses electrical or magnetic fields to determine the position and orientation of a catheter within the heart. One example of such as visualization, navigation, or mapping system is the EnSite NavX system comprising hardware and software available from St. Jude Medical of St. Paul, Minn. This system creates a geometric model by tracking the electrical impedance of a mapping catheter in three different directions. The three dimensional map is then constructed with reference to a static reference electrode. The reference electrode allows the mapping device to compensate for voluntary shifting by the patient, such as from localized discomfort, and to compensate for involuntary movement, such as breathing, thereby creating a more stable model.
However, electrical navigational fields are not assured to be homogeneous or isotropic, so it is common for these geometric models to face the challenge of spatial distortion. Further complicating the location of ICE catheters and the images they produce is the fact that any variations in the positioning and orientation of the electrodes with respect to the ultrasound transducer result in apparent translational and rotational positioning errors. An angular misalignment resulting from a rotational positioning error causes a spatial discrepancy between the actual and displayed locations. The discrepancy from angular misalignment increases the further from the ultrasound transducer an object is located. Thus, even moderate rotational error can result in significant positioning error for structures appearing at the edge of an echo image.
It is well known that intracardiac echo catheters provide images of cardiac structures and, under some conditions, other intracardiac catheters. The metal electrodes present on intracardiac catheters are very echogenic and produce bright signatures in echo images, particularly when the catheter shaft is not axially aligned with the echo plane or when the catheter shaft lies in the plane of the echo beam and is oriented perpendicular to it. However, identification of another catheter alone is seldom sufficient to locate the ICE catheter and may not allow the accurate projection of the ICE echo image into a geometric model created with electric or magnetic field modeling.
The inventors herein have thus recognized a need for a system and method for precise and real-time location of ICE catheters and the images they produce within geometric models of the heart, or within the heart itself, to allow physicians to easily obtain ICE images of cardiac structures and/or other intracardiac catheters of interest to allow accurate and effective therapeutic treatment.